uclibc-ng/libpthread/nptl/sysdeps/unix/sysv/linux/sem_post.c

/* sem_post -- post to a POSIX semaphore.  Generic futex-using version.
   Copyright (C) 2003, 2004, 2007, 2008 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <errno.h>
#include <sysdep.h>
#include <lowlevellock.h>
#include <internaltypes.h>
#include <semaphore.h>
#include <tls.h>

int
sem_post (sem_t *sem)
{
  struct new_sem *isem = (struct new_sem *) sem;

  __typeof (isem->value) cur;
  do
    {
      cur = isem->value;
      if (isem->value == SEM_VALUE_MAX)
	{
	  __set_errno (EOVERFLOW);
	  return -1;
	}
    }
  while (atomic_compare_and_exchange_bool_acq (&isem->value, cur + 1, cur));

  atomic_full_barrier ();
  if (isem->nwaiters > 0)
    {
      int err = lll_futex_wake (&isem->value, 1,
				isem->private ^ FUTEX_PRIVATE_FLAG);
      if (__builtin_expect (err, 0) < 0)
	{
	  __set_errno (-err);
	  return -1;
	}
    }
  return 0;
}